1. Field of the Invention
The present invention relates to a charging device for a battery, and in particular to a battery charging device for charging and rejuvenating a primary cell, such as a zinc-manganese alkaline battery.
2. The Prior Art
As technologies progress, electronic devices have been applied to various fields, especially to portable devices, such as radios, portable video game players, mobile phones, video cameras, cameras and electronic toys. Generally speaking, these portable devices need batteries to provide power. Primary cells (disposable batteries), such as zinc-carbon batteries and zinc-manganese alkaline batteries, are widely used because of their low cost and constant output electric power.
When discharging, the internal resistance of the primary cell will increase due to the electrochemical reaction. Thus, the output voltage decreases. When the output voltage decreases to a critical voltage, the output voltage is not large enough to make an electronic device work normally. Although the primary cell can still provide a smaller output voltage, the primary cell having a smaller output voltage is replaced with a new one. Also, the primary cell can not be reused, therefore it is thrown away. Annual yield of primary cells is numerous, and therefore the discarded primary cells cause a great burden on the environment.
Although secondary cells (rechargeable batteries), such as nickel-metal hydride batteries, nickel-cadmium batteries and lithium-ion batteries, may be reused through charging, the price of the secondary cells is much higher than the primary cells. It takes about 4 to 8 hours to fully charge the secondary cells, and the secondary cells can only be charged less than 100 times. The secondary cells have other disadvantages. Take a nickel-metal hydride battery as an example, it has a voltage of 1.2V, which is different from the 1.5V of a primary cell, thus it may not be used in certain electric appliances needing higher starting voltage. As for a lithium-ion battery, it has a risk of explosion. The United States even ban spare lithium-ion batteries of laptop computers in checked luggage when taking a flight. Therefore, there is a need to provide a charging device for a primary cell that can charge and rejuvenate the primary cell, and increase the output voltage.